Apparatus for treating pulp



1,633,553 June 1927' c. H. ALLEN APPARATUS FOR TREATING PULP inal Filed Dec. 29, 1919 2 ets-Sheet 1 June 21, 1927.

C. H. ALLEN APPARATUS FOR TREATING PULP Original Filed Dec. 29, 1919 2 Sheets-Sheet 2 #IIIIIIIIP Fig. 5.

Patented June 2l, 1927.

UNITED STATES CARLTON H. ALLEN, OF

NORTHERN PAPER COMPANY, OF MILLINOCKET, MAINE, A

MAINE.

MILLINOCKET, MAINE, ASSIGNOR OF ONE-HALF TO GREAT CORPORATION OF APPARATUS FOR TREATING PULP.

Application filed Deeember 29, 1919, Serial No. 348,059. Renewed November 80, 1888.

The usual process of manufacturin chemical pulp consists in introducing woo in the form of chips into suitable digesters together with a solution of the mono-sulphites and bi-sulphites of calcium and magnesia in sulphurous acid. The digester is then tightly closed and steam is admitted at the bottom of the digester for a number of hours at a varying rate. This addition of heat breaks up the sulphurous acid intoyvater and the sulphur dioxide gas collecting at the top of the digester causes the pressure in the digester to increase to such a point that it must be relieved in order to prevent interference with the cooking of the charge, and to make room for the introduction of more steam. For the same reason it is necessary also to draw off a certain quantity of the liquid in the digester as the reaction progresses since the condensation of the steam adds substantially to the volume of the liquid present.

The temperature and pressure maintained in the digester at succeeding intervals of time while the cooking operation progresses determines to a marked degree the yield of fibre obtained from the wood and also the quality of the resulting pulp. That is, if too high a temperature -is maintained the cellulose is attacked by the acid, thus spoiling or destroying some of it and thereby redueing the yield of good fibre. On the other hand. if the temperature is too low the length of time necessary to complete the cooking reaction is unduly increased, and a part of the lignin, or. material binding the woody fibres together, is not dissolved. This result is known in the trade as a raw cook.

The present practice is to give the attendant detailed directions as to the temperature and pressure desired at succeeding intervals of time and to use recording temperature and pressure gages to keep a record of the progress of each charge or batch which is cooked, relying upon the care and skill of the attendant to so adjust the valves controlling the admission of steam to the digester and the relief of gas and liquor therefrom, as to maintain the desired temperature and pressure conditions during the entire treatment of the charge.

It is the chief object of the present invention to devise an apparatus for treating pulp n t(li1is manner which will maintain the desire automatically during the cooking of the charge. In other words, the invention aims to replace the uncertain manual control, which must now be relied upon, by an automatic control, and thus to produce greater uniformity in results and to effect an increased economy in the practice of the process.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings and the novel features will-be particularly pointed out in the appended claims.

Referring now to the drawin Figure 1 is a diagrammatic v1ew showing the general organization of an apparatus embodying the present invention;

Fig. 2 is a plan view illustrating one of the valves and the mechanism for automatically operating it;

Fig. 3 is an elevation, partly in cross section, of a part of the apparatus shown in Fig. 2;

Fig. 4 is a view partly in side elevation and partly in cross section of the valve operating mechanism shown in Fig. 2; and

Fig. 5 1s a diagrammatic view of a modified form of apparatus similar to that shown in Fig. 2.

Briefly stated, the apparatus shown oomprises a digester, a steam supply line for delivering steam to the digester, and a novel mechanism for controlling the admission of steam throu h this line to the digester, this mechanism eing designed to maintain a predetermined temperature which, however, varies at succeeding intervals of time during the period required to cook a charge. The apparatus also includes means for releasing gas and liquid from the digester automatically as required to maintain substantially predetermined pressure conditions in the digester while the charge is being cooked. Provision, furthermore, is made for separating the gas and liquor released from the digester, and for conducting them to separate reservoirs where they are utilized in subsequent operations. I

The apparatus shown comprises a digester 2 of the type commonly employed in cooking pulp. A steam line 3, in which is connecte a steam separator 4 and a pressure reducing valve 5, delivers steam to the lower part of the digester 2. The digester may be drained through a valve 6 and a pipe connection leading therefrom.

The flow of steam to the digester is controlled by a valve 7 which is automatically operated by a mechanism best illustrated in Fig. 2. This mechanism comprises an instrument 8 like a steam flow recorder except that the usual dial is replaced by a dial 9 which is mounted fast on a spindle 10 that is driven by a clock mechanism. The instrument also includes a pivoted arm 11 like the pen holding arm of a steam fiow recorder and operated in the same manner by variations in the How of steam through the pipe line 3, the instrument for this purpose being connected with the steam line by the pipes 12, Fig. 1. The dial 9 consists of two sections X and Y, respectively, electrically insulated from each other by insulation 14. and also electrically insulated from the spindle 10, as shown in Fig. 3, but mechanically secured to said spindle so that the dial rotates with the spindle. The edges of these sections are shaped to form a cam slot 15 between them in which travels a pin 16 mounted on the end of the arm 11 but insulated from said arm. This pin is connected by an electrical conductor 17 with one terminal of a source 18 of electricity. The two sections X and Y of the dial are connected by conductors 19 and 19', respectively, to solenoids 20 and 21, the opposite terminals of these solenoids being connected to a common conductor 22 that runs to the opposite terminal of the source 18 of electricity.

It will now be evident that when the pin 16 strikes either side of the cam slot 15 it will complete an electrical circuit through one or the other of the solenoids 20 and 21, depending on whether the pin engages the section X or Y of the dial. These instrumentalities control the operative connection between a mechanism that moves the valve 7 and power driven means for operating sai mechanism. For this purpose the stem 24 of the valve 7 is provided with a threaded portion 25 on which is mounted a ratchet wheel 26 that engages the threads of the part 25 and rotates between two stationary arms of a bracket 27 secured to the support for this part of the apparatus. This construction enables the ratchet Wheel to turn on the valve stem and causes this rotative movement to slide the valve stem axially in one direction or the other.

Oppositely directed teeth are cut in the lateral faces of the ratchet wheel 26. as clearly shown in Figs. 2 and 4. Straddling one edge of this ratchet is a double pawl 28 which is hung on a pin projecting eccentrid finger 38 cally from a disk 29 mounted fast on a shaft 30 to which also is fixed a pulley 31 by means o which the shaft may be driven continuously from any convenient source of power. The pawl carries points and 33, respectively, for engagement with the teeth on the ratchet wheel 26, and this engagement is controlled by the solenoids 20 and 21 through a T-shaped lever 34, one arm of which is connected with the pawl 28 by a rod 35 and the other arms of which are connected to the cores of the respective solenoids.

Springs 36 and 37 normally hold the lever 34 in a central or neutral position and, through the connections with the pawl 28, the latter member at this time is held in such a position that neither the pawl points 32 or 33 can engage the ratchet wheel. Consequently, so long as the parts remain in this condition no operative movement of the valve stem is produced, the pawl simply reciprocating idly. Vhen, however, one o the solenoids 20 or 21 is energized by the engagement of the pin 16 with one of the dial sections X and the lever 34 is tipped on its fulcrum thus moving the pawl 28 into position to enable one or the other of the points 32 or 33 to engage the ratchet wheel 26 and impart to this wheel a step by step rotation. This movement opens or closes the valve 7 depending upon the direction of rotation of the Wheel 26, and this adjusting movement of the valve continues until the solenoid is again de-energized, when the springs 36 and 37 restore it to its neutral position and thus interrupt the operative engagement of the pawl 28 with the ratchet wheel 26.

As a safety or limiting device the valve stem 24 carriestwo fingers 38 and 39 which are spaced apart and are adjustably secured to the stem. The parts are so arranged that when the solenoid 20 is energized the rod 35 will be moved toward the right, as the parts appear in Fig. 2, bringing the pawl point 32 into contact with the ratchet wheel 26 and thus opening the valve, and when this opening movement has been nearly completed the will engage a pin 40, Fig. 4, projecting from the lever 34 and will tip this lever back. into its neutral position even though the solenoid 20 still remains energized. The finger 39 operates in the same manner upon the closing of the valve. These parts thus stop the adjusting movement of the valve automatically at predetermined limits.

It will now be evident that this mechanism operates automatically to supply steam at a predetermined but variable rate to the digester 2 during the period of time required to cook a charge, the rate of steam flow at successive intervals of time being determined by the shape of the cam slot 15 so that this rate can be changed by removing the dial 9 I ture can be varied and substituting another one having a differntly shaped cam slot. The mechanism thus supplies automatically the quantities of steam required at successive intervals of time to properly cook the charge.

As above stated, the steam condensed in the digester adds substantially to the volume of the liquid therein. This, together with the sulphur dioxide gas liberated while the cooking operation is progressing, increases the pressure in the digester to an undesirable degree. Provision therefore is made by this invention for automatically relieving the pressure as may be necessary to maintain predetermined pressure conditions while the charge is being cooked and for varying the pressure at successive intervals of time as required to secure the best results. For this purpose a discharge pipe line 41 leads from the top of the digester and the flow of fluids through this pipe is controlled by a valve 42 which is operated by a mechanism similar to that above de scribed for operating the valve 7. The instrument 43 of this mechanism is constructed substantially like a pressure recording gage, but the dial of this instrument is of the same general construction as that of the instrument 8 and the arm 44 is operated by variations in pressure in the digester, the instrument for this purpose being connected with the digester by a pipe 45. This mechanism thus operates automatically to open, or partly open, the valve and relieve the pressure if the pressure at any time becomes excessive and to close or partly close, the valve automatically again when the pressure has been reduced to substantially the desired point.

It is desirable to'save the gas and liquor that are discharged through the pipe 41 and for this purpose the pipe 41 is led into a separator 46 of any suitable form, the liquor flowing by gravity from this separator into a U-shaped pipe 47 which constitutes a trap. From this trap the liquor flows through a cooler 48 and thence through the pipe 49 into the raw acid tank 50. The trap 47 prevents the gas from flowing into the tank 50. A pipe 51 leading from the separator 46 conducts the gas through a gas cooler 52 into a reclaiming tank 53.

If desired, the mechanism that controls the valve 7-instead of being responsive to variations in steam flow can be made responsive to variations in the temperature in the digester so that the valve 7 will be operated automatically to so. regulate the flow of steam that predetermined temperature conditions will be maintained during the cooking of the charge. At the same time this temperaautomatically in a predetermined manner at successive intervals of time. An apparatus designed to perform this function and which also embodies a responding to the arm 11 of the gage 8,

Fig. 2, is moved by variations in temperature within the digester. The dial 57 IS insulated from but rotates with the spindle 58 of the instrument, this spindle being driven by clock work, and the dial is electrically connected by a conductor 59 with a solenoid 60. The other terminal of this solenoid is connected to one pole of the source 61 of electricity, the other pole of said source of electricity being connected by a conductor 62 to a pin 66 mounted in the end of the arm 56. In other respects the operating mechanism of the valve is like that shown in Fig. 2 except that the pawl 28 is connected directly by the link with the core of the solenoid and by a spring 64 that is also connected directly to a pawl. \Vhen the solenoid 60 is energized through the engagement of the pin 66 with the edge of the cam-shaped dial 57, the pawl 28 will be held in position to effect an opening movement of the valve 7 until the finger 38 on the valve stem 24 engages a pin 65 on the link 63 and moves the pawl 28 back into its neutral or inoperative position. The parts remain in this position so long as the solenoid remains energized but as soon as it becomes de-energized, due to the interruption of engagement of the cam 57 with the pin 66, the spring 64 swings the pawl 28 in the opposite direction and thuseflects a closing movement of the valve 7 which movement, however, is interrupted by the engagement of the finger 39 with the pin 65. It is obvious that this valve operating mechanism is somewhat simpler than that shown in Fig. 2, the dial of the instrument being'of a simpler construction and the mechanism controlled thereby also being simpler.

It will now be understood that this invention provides an apparatus which operates automatically to maintain the temperature and pressure conditions desired in the digester during the entire period necessary to cook the charge thus making it entirely unnecessary to rely on the care or skill of an attendant tomake the manual adjustments heretofore required to accomplish this object. The invention, therefore, is of advantage not only in reducing the labor cost of the pulp making operation but because it produces a better yield of fibre and a more uniform quality of pulp.

This application contains certain subject matter in common with my copending application Serial No. 530,140, filed January 18, 1922, and the broad claims on said common subject matter are presented in the latsubstantially ter case, the claims of the present application being confined to features which are not disclosed in my later application.

What is claimed as nevi is:

1. A pulp treating apparatus of the character described comprising, in combination, a digester, means for supplying steam to said digester, means for automatically controlling the supply of steam to said digester and additional means for automatically controlling the discharge of fluids from said digestcr, said means cooperating to maintain predetermined temperature and pressure conditions in said digester during a predetermined interval of time.

2. A pulp treating apparatus of the character described comprising, in combination, a digcster, means for supplying steam to sail digester, automatic means for controlling the supply of steam to said digester to maintain substantially predetermined but variable temperature conditions in said digester during a predetermined interval of time, a discharge pipe leading from said digester, a valve controlling the flow of fluids through said pipe, and means for automatically operatin said valve to maintain substantially pred etermined pressure conditions in said digester during a predetermined interval of time.

3. A pulp treating apparatus of the character described comprising, in combination, a digester, means for supplying steam to said digester, means for automatically controlling the supply of steam to said digester, and additional means for automatically controlling the discharge of fluids from said digest/er, said. automatic means cooperating to maintain substantially predetermined pressure'and temperature conditions in said digest/er during a predetermined period of time and for varying said temperature and pressure conditions in a predetermined manner at successive intervals of time during said period.

In testimony whereof I have signed my name to this specification.

CARLTON H. ALLEN. 

